bHLH proteins are commonly found to interact with other bHLH proteins as heterodimers to regulate gene expression and a potential hypothesis for the role of TAL1 in T ALL is that overexpression of TAL1 and its mutants disrupt the normal gene program by interacting with other transcription factors that regulate T cell development such as E2A proteins (98). Here, TCF3 is linked to acute lymphoblastic leukemia.